This invention relates generally to furnace exhaust gas systems and more specifically is directed to an all-mechanical, self-operated draft controller for a fuel-burning appliance, or a furnace, which eliminates the heat loss of a conventional draft hood.
A draft hood is typically used in a conventional gas-fired appliance such as a furnace or a water heater. The draft hood generally includes a housing which couples the appliance's firebox with the flue pipe, or exhaust stack, by means of which the products of combustion from the firebox are safely vented to the atmosphere. In some installations, the draft hood may be positioned in the exhaust stack itself.
The conventional draft hood performs a variety of functions in a gas-fired appliance. It permits the escape of combustion products into the space adjacent the draft hood in the case of an excessive down draft or flue pipe or exhaust stack blockage beyond the draft hood. The draft hood also neutralizes the stack action of the chimney on the operation of the appliance by drawing air from the ambient and exhausting it through the chimney when the appliance is first fired. Thus, the draft hood plays an integral part in the initiation and sustaining of combustion in the appliance by controlling air flow in the firebox.
Draft hoods have long been known to also provide a readily available escape route for heated room air thus contributing to substantial heat loss in conventional gas-fired heating appliances. In the past, the low cost of fuel has mitigated against reducing draft hood heat loss or completely eliminating the draft hood. In addition, the safety and reliability provided by the conventional draft hood was particularly attractive in the residential environment.
Even with increasing fuel costs, the draft hood has remained an integral part of the conventional gas-fired heating appliance primarily because of its aforementioned attributes, i.e., safety, low cost and high reliability.
Today, however, much effort is being expended by heating appliance designers to reduce energy losses in general, and those attributable to the draft hood of the appliance in particular. In order to achieve higher energy efficiency based upon governmental standards, work is currently under way on the design and development of pulse burners, induced draft closed combustion chambers and other methods of eliminating draft hood losses. To date, these efforts have resulted in systems which are more expensive, noisier, and much less reliable than currently available draft hoods. Thus, there is currently a great need for a simple yet reliable, inexpensive yet energy efficient, independently self-actuated means for eliminating or substantially reducing the large energy loss characteristic of current draft hoods in conventional gas-fired heating appliances.
The present invention is intended to provide these advantages over a conventional draft hood and is easily installed, even by means of retrofit, in the typical residential gas-fired heating appliance.